DE1913725C3 - Use of sulfenamide compounds to inhibit premature vulcanization of vulcanizable rubber compounds - Google Patents

Description

20th

In the manufacture of vulcanized rubber products, raw rubber is used with various other ingredients, such as fillers, accelerators and protective agents against degradation or deterioration, mixed to processing the rubber to 2s facilitate and improve the properties of the finished product. The raw rubber is thereby through various stages performed before it is ready for the final stage of vulcanization. In general, the Rubber initially with carbon black and other components, apart from the vulcanizing agent and accelerator, Then the vulcanizing agents and accelerators are mixed in with this master batch added to a Banbury mixer or a rolling mill. Burning, the so-called scorching, that is, premature vulcanization, can occur at this stage of processing, during storage before Vulcanization and take place during the actual vulcanization.

After adding the vulcanizing agents and accelerators, the mixture is ready for calendering or Extruding and Vulcanizing Ready If premature vulcanization occurs during storage of the Mixing or processing takes place before vulcanization, the processing operations not be done because the burned or precured rubber is rough and lumpy and so that is worthless

Premature vulcanization poses in the rubber industry the main problem and must be prevented in order to avoid deformation and shaping of the Allow rubber mixture before curing or vulcanization.

The discovery of thiazole sulfenamide accelerators represented a significant advance in vulcanization technology in that thiazole fullfenamide delayed the start of the vulcanization process. Once this had started, however, the amine activation adhering to the thiazole led to strong and rapid vulcanization. _bü

Mercaptobenzothiazole is another more valuable one organic vulcanization accelerator. When using this accelerator, however, the do not avoid unwanted pre-vulcanization; especially since then through the development and use (, 5 The formation of carbon blacks with high pH values and the largely popular use of Phenylenediamine anti-degradation agents made higher demands on the vulcanization accelerator system will.

Systems containing mercaptobenzolthiazole were therefore partly used by other accelerator systems retarding effect replaced, d. h, it was special Vulcanization retardant added to the vulcanization mixture in addition.

These are compounds such as N-nitrosodiphenylamine, salicylic acid or a terpene-resin acid mixture. However, acids as vulcanization retardants are used together with thiazole sulfenamide accelerators generally ineffective or adversely affect the vulcanization process.

On the other hand, nitrosoamines have only limited effectiveness with thiazole sulfenamides.

From the FR-PS are sulfenamides and their use as inhibitors of premature vulcanization known from rubber mixtures These sulfenamides are predominantly N-alkylthio- or N-arylthio derivatives of dicarboximides, such as N- (cyclohexyl-thio) phthalimide.

It has now surprisingly been found that sulfenamides derived from monocarboxamides surprisingly more effective agents for retarding premature vulcanization than the products the FR-PS15 00 844.

The invention therefore relates to the use according to claim.

The effect as an inhibitor of premature vulcanization does not seem to depend on the nature of the mercapto radicals bonded to the nitrogen atom, but whether the rest of the molecule is a Represents a carboxamide group or a dicarboximide group

The cycloalkyl group R of the general formula given in the claim preferably contains 5 up to 8 carbon atoms.

N, N-di- (phenylthio) -acetamide and N- (phenylthio) -benzamide are preferably used

The invention is explained in more detail by the following tables and examples. at all of the following rubbers are given the Mooney Scorch times at 12PC and 135 ° C using of a Mooney PI astrometer and the time in minutes (fs) required for the Mooney dimensions to increase by 5 points above the minimum viscosity required is longer Times are a measure of the activity of the inhibitor. Longer durations in Mooney Scorch Times are desirable because this is a sign of greater processing security

The percentage delay in scorching is calculated by taking the Mooney scorch time of the The mass containing the retarder or inhibitor divided by the Mooney Scorch time of a comparative mass, multiplied by 100 and subtracted 100

The results show the percentage improvement in the scorch retardation compared to the comparison material which contains no retarder or inhibitor. In addition, vulcanization ratings are calculated from the time taken to vulcanize the Masses at 144 ° C and in some cases at 153 ° C is required. The vulcanization properties will be with the help of a Monsanto rheometer, which is described in the magazine "Rubber World" (1962), page 68 is determined

Of the rheometer values, R.M.T. is the maximum Rotation in rheometer units, ft or fe is the

Time in minutes for an increase of 2 or 3 rheometer units above the minimum reading, and Γ90 is the amount of time it takes to rotate 90% of the maximum is required. The following Table I illustrates the results using N, N-Di (phenylthio) acetamide as an inhibitor against premature vulcanization in masses of natural Katuschuk, the N, N'-bis (1,4-diinethyl-pentyI) -p-phenylenediamine as an antioxidant and 2- (morpholinothio) -benzothiazole included as an accelerator.

From the values in Table I it can be seen that N, N-di (phenylthio) acetamide in the presence of the accelerator is very effective as an inhibitor against premature vulcanization

Table I.

10

15th

Dimensions B. 20th A. 100 Natural rubber 100 50 Highly abrasion-resistant furnace soot 50 5 Zinc oxide 5 3 25th Stearic acid 3 10 Hydrocarbon plasticizers 10 2.5 sulfur 24 W-bis-iM-dimethylpentyl) - 3 p-phenylenediamine 3 04 30th 2-morpholinothio-benzothiazole 04 1.0 N, N- (Diphenylthio) acetamide Rheometer at 144 ° C 154 U 27.2 35 '90 18.0 0.187 0.183 56.5 R. M. T. 545

Annotation:

*) Ar is a specific rate constant, measured in reciprocal minutes (see the journal "Rubber Chemistry and Technology" [1964], p. 689).

The following table II shows that the compound N- (phenylthio) -benzamide is an inhibitor against premature Vulcanization is The connection is tested in a master batch of the following composition.

Table II Trunk approach

sulfur

2-morpholinothiobenzothiazole

N-13-dimethylbutyl-N'-phenyl-

p-phenylenediamine

N- (phenylthio) benzamide Mooney scorch at 121 ° C Percentage increase in Scorch delay

Rheometer at 144 ° C
RMT

Dimensions 2 50 1 155
2.5
0.5 155
24
04 2.0
1.0 55 2.0 85.3 35.2 144 60 - 63.8
20.0
39.2 61.0
8.7
27.7 b5

Rubber compositions containing delayed action accelerators can also be used. Cheaper accelerators with larger) scorching can also be used and result in a excellent improvement.

The invention is applicable to rubber compounds containing sulfur vulcanizing agents, peroxide vulcanizing agents, organic accelerators for vulcanization and anti-degradation agents, none of which used inhibitor is included.

Under "sulfur vulcanizing agent" is more elementary here Sulfur or a sulfur-containing vulcanizing agent such as an amine disulfide or a Polysulfide, understand.

The invention is applicable to vulcanization accelerators of various classes. For example can Rubber compounds containing aromatic thiazole accelerators, including

Benzothiazyl-2-monocyclohexylsulfenamide,
2-mercaptobenzothiazole,
N-tert-butyl-2-benzothiazolesulfenamide,
2- Benzo thiazolyl diethyldithiocarbamate and
2- (Morpholinothio) -benzothiazole,
be used. Amine salts of mercaptobenzothiazole accelerators such as the tert-butylamine salt of mercaptobenzothiazole or 2,6-dimethylnorpholine can be used. However, other thiazole accelerators can also be used. Compositions containing accelerators, such as tetramethylthiuram disulfide, tetramethylthiuram monosulfide, aldehyde-amine condensation products, thiocarbamylsulfenamides, thioureas, xanthates and guanidine derivatives, are significantly improved by the use according to the invention of the compounds of the general formula. The compounds of the above general formula can be natural and synthetic rubber materials Mixtures thereof are added.

Examples of synthetic rubber materials are cis-4-polybutadiene, butyl rubber, ethyl-propylene terpolymers, Polymers of 1,3-butadiene, such as 1,3-butadiene itself, and of isoprene, copolymers of 1,3-butadiene with other monomers such as styrene, acrylonitrile, isobutylene and methyl methacrylate

Concentration studies show that the compounds of the above general formula are effective in rubber at concentrations of 0.05 to 5.0 parts per 100 parts of rubber. Concentrations but from 0.10 to 3.0 parts per 100 parts are preferred

Making the
compounds used according to the invention

example 1

Benzene sulfochloride (0.20 mol) in 40 ml of dimethylformamide is added dropwise at room temperature to acetamide (0.20 mol) and pyridine (0.20 mol) in 100 ml of dimethylformamide. An exothermic reaction takes place which ^{causes the temperature to rise to 38 °} C. After stirring for 1 hour, the mixture is poured into 1 liter of water. The red, separating oil is extracted with chloroform. The chloroform extract is washed with water, dried over sodium sulfate and stripped in vacuo to a liquid residue. After adding 100 ml of heptane to the residue, it crystallizes out. There were N- (phenylthio) acetamide with a mp.

98 to 102 ⁰ C obtained by filtration. The compound was recrystallized from heptane and melted at 104.2 to 105.0 ⁰ C

Analysis for C ₈ H ₉ NOS:

Ben: C 57.46%, H 5.42%, N 838%, S 19.17%;
Found: C 5738%, H 5.53%, N 834%, S 18.91%.

Example 2

N ^ CydohexylthioJ-acetam-d is prepared by reacting cyclohexylsulfenyl chloride and acetamide in the presence of pyridine. The desired product had a melting point of 63 to 64 ° C. Another suitable method involves the reaction of cyclohexylsulfenyl chloride with a salt of acetamide. Acetamide (03 mol) and sodium methoxide (03 mol) are heated in methanol until the acetamide dissolves. The mixture is then stripped off in vacuo, and sodium acetamide is obtained, which is then suspended in 50 ml of heptane. Cyclohexanesulfenyl chloride (03 mol) in 300 ml of heptane is added to the stirred slurry. After part of the sulfenyl chloride has been added, 100 ml of dimethylformamide are added to dissolve the sodium acetamide, and the remainder of the sulfenyl chloride is added. The mixture is stirred for 30 minutes and 600 ml of water are added, the heptane layer is separated off and the aqueous portion is extracted with it Chloroform. The heptane and chloroform solutions are combined, washed with water, fiber sodium sulfate and concentrated in vacuo The residue is taken up in 100 ml of heptane and cooled for crystallization to -7O ⁰ C. The crystals are collected by filtration. After recrystallization from heptane, the N--cyclohexylthioJ-acetamide obtained melted at 663 to 66.8 ° C

Analysis for C ₈ Hi ₅ NOS:

Calc .: C 55.45%, H ', 73%, N 8.08%, S 18.50%;
Found: C 5536%, H ', 49%, N 8.06, S 18.30.

was concentrated The oil is slurried in 100 ml heptane and by adding 30 ml of ether crystallized the product is collected by filtration and recrystallized from a ÄtLanol-water mixture recrystallized The resulting N- (cyclohexylthio) benzamide had a melting point 107-108 ⁰ C.

Analysis for CuHi ₇ NOS:

Ben: C 6635%, H 7.28%, N 5.95%, S 13.62%;
_{) o found} : C 65.63%, H 7.18%, N 5.86%, S 13.77%.

Example 4

Cyclohexylsulfenyl chloride (0.5 mol) is added dropwise within 1 hour at 25 to 40 ⁰ C to a solution containing n-butyramide (0.5 mol) and triethylamine (0.5 mol) in 200 ml of dimethylformamide. / Stirred for 2 hours and the amine salt by-product is removed by filtration. The filtrate is added to 1 liter of water. The product is then extracted with heptane, dried over sodium sulfate and N- (CycIohexylthio) butyramide is obtained as an oil with the aid of a rotary evaporator. The yield was 60 g. Infrared analysis showed a carbonyl band at 5.92 microns.

25th

35

40

Example 3

N- (Cyclohexylthio) -benzamide is produced in the presence of an acid acceptor, the sulfenyl chloride but is reacted with a salt of benzamide as follows: Butyllithium (0.05 mol) is approximately 50 ml of hexane within 20 min. To a solution of benzamide (0.05 mol) in about 400 ml of anhydrous Benzene was added, forming a thick white precipitate. After stirring for 5 minutes, it was added Cyclohexanesulfenyl chloride (0.05 mol) in heptane added at room temperature within 10 min The mixture is then stirred for a further 30 minutes and filtered. The filtrate is vacuum stripped and obtained a crude product The residue is dissolved in 200 ml of ether and used to remove a small amount of insoluble salt filtered. The filter is dried over sodium sulfate and returned to an oily return table III

Example 5

To a solution containing n-butyramide (0.5 mol) and triethylamine (0.5 mol) in 200 ml of dimethylformamide Benzolsulfenylchlorid (0.5 mol) was added dropwise within 45 minutes. After stirring for 15 minutes The amine salt by-product was removed from the mixture by filtration. The filtrate was dissolved in 1 liter of water quenched, the product extracted with 200 ml of benzene, dried over sodium sulfate and filtered. The benzene was removed using a rotary evaporator and 75.5 g of N- (PhenyIthio) -n-butyramide with a melting point of 52 to 53 ° C. (from xylene recrystallized). The compound was determined by nuclear magnetic resonance analysis identified

The compounds used according to the invention were tested in a masterbatch, the following one Composition showed:

Smoked sheets Intermediate-highly abrasion-resistant

Furnace soot

Zinc oxide

Stearic acid Aromatic emollient oil

Parts
100

45
3
2
5

The following table shows the effect of the compounds used according to the invention in materials of natural rubber, the phenylenediamine anti-degradation agent and N-tert-butyl-2-benzothiazole sulfenamide accelerators contain. The comparative sample (not shown) did not contain any inhibitor. The values obtained for the comparative sample are in Table III listed under 1

Masterbatch
sulfur

material 2 3 4th 5 6th 7th 1 155 155 155 155 155 155 155 2 2 2 2 2 2 2

7 8

continuation

material
1 2

N-tert-but> l 2-benzothiazokulfenamide 0.5 0.5 0.5 0.5 0.5 0.5 0.5

N-1,3-dimethylbutyl-N'-phenyl- 2 2 2 2 2 2 2

p-pheny! endiamine

N- (Phenylthio) -benzamide 0.5 ----- -

N- (phenylthio) acetamide 0.5 - - -

N, N-Di- (phenylthio) -acetamide - - 0.5 - - - -

N- (Cyclohexylthio) acetamide - 0.5

N-iCyclohexylthioJ-benzamide - - 0.5 -

N- (phenylthio) -n-butyramide - ■ - - - 0.5 -

N-iCyclohexylthioJ-phthalimide ------ 0.5

Mooney Scorch at 121 C / ₅ , min. Percentage increase in scorch delay

Rheometer at 144 C RMT h / 90

The table shows the superiority of the compounds used according to the invention over that from French patent 15 00 844 known N- (cyclohexylthio) phthalimide.

61.3 71.6 81.0 106.6 88.5 60.0 96.2 82 112 137 . 212 159 96 181 50.0 51.0 49.5 49.5 50.0 61.0 48.8 12.5 13.3 18.3 20.7 17.8 14.0 19.9 23.6 24.5 32.0 34.7 32.4 26.0 33.5

Claims (1)

Claim: Use of compounds of the general formula C- /. N (-SR) _n . in which η and n 'is 1 or 2 and n "0 or 1 and the sum of η, η' and π" is 3 and the radicals R is an aryl, alkyl or cycloalkyl group and X is a hydrogen atom, to inhibit the premature vulcanization of vulcanizable rubber compounds which contain a common vulcanizing agent and a common vulcanization accelerator and a common stabilizer.